Since the manufacturing cost of the driving mechanisms utilizing step motors are not only much cheaper than that of the driving mechanisms utilizing DC motors, but also the driving mechanisms utilizing step motors are more suitable for high velocity seeking, the optical disk drive using step motors for driving the optical head thereof has become the mainstream product in the recent years.
Conventionally, while a step motor is being used to drive the optical head of an optical disk drive, the profile of the velocity profile generator arranged in the step motor control device is usually being designed to accelerate or decelerate very rapidly so as to reduce the seek time in a long seek operation. Under the circumstance, the rotation inertia of the step motor is becoming larger such that the resonant effect is becoming considerably obvious. As the result, the optical head is difficult to lock on a track after the seeking.
Please refer to FIG. 1, which is a schematic drawing of a conventional long seek control device for an optical disk drive. The control device 100 comprises two independent parts. One is a step motor control device 110 capable of controlling a step motor 105 while performing a long seek operation. The other one is an optical head control device 120 capable of controlling an optical head 107 to remain in the center of the mechanism therein while performing the long seek operation.
While performing a long seek operation, the velocity profile generator 111 arranged in the step motor control device 110 will control the motion of the step motor 105 by way of a frequency converter 115, a sinusoid generator 117, and a driver 118 according to the received output information signals 113, such as seek total and seek direction, and so on. Meanwhile, the center error controller 121 in the optical head control device 120 receives a center error signal (CE) to output a seek control signal 123 and controls the optical head 107 to remain in the center of the mechanism therein through the driver 125.
Wherein, the velocity profile generated by the velocity profile generator 110 used for controlling the step motor 105 typically is a ladder shaped profile for conforming to the fast acceleration and deceleration requirements. Please refer to FIG. 2, which is the velocity profile of a conventional velocity profile generator used for controlling the step motor. The step motor 105 starts to accelerate when the long seek begins (0˜t1), and maintains at a fixed velocity (t1˜t2) afterwards, and starts to decelerate before the long distance seek finishes (t2˜t3).
Since the optical head control device 120 is using the center error signal during the period of t2˜t3, i.e. the long seek is going to finish, the disk that the optical head 107 is seeking is vulnerable to run-out effect such that the optical head 107 is difficult to lock on a track after the seeking.
The conventional method used to reduce the run out effect happening at the end of the seeking, that is, during the period of t2˜t3, is to reduce the slope of the velocity profile at the t2˜t3 period such the optical head is able to lock on a track easier. However, this method will lengthen the seek time.
In view of the above description, the present invention provides a long seek control device for optical disk drive and method thereof capable of locking on a track properly after seeking and therefore preventing the slipping from happening.